The present invention relates to a holder for a lens system that is suited to an image display device that magnifies and projects, onto a screen, an image displayed on a light modulator, such as a liquid crystal display device, a DMD, or the like, to a lens unit in which such lens system is incorporated, and to an image display device having such lens unit.
A lens unit used in a camera, projector, or the like is produced by holding a lens system composed of a plurality of lenses in a cylindrical holder which is then incorporated in an apparatus. Japanese Laid-Open Patent Publication No. 2002-40308 discloses a lens apparatus constructed by holding a plurality of lenses in lens holding cylinders with the lenses sandwiched between contact surfaces of the lens holding cylinders and pressing rings.
To hold a plurality of lenses at predetermined positions, the above lens apparatus needs to have a large number of lens holding cylinders and a large number of pressing rings. This means, not only a large number of components but also a considerable time are required for assembling.
Also known is a rear-projection-type projector (hereinafter simply “rear projector”) that uses a projection lens to project projecting light from a light modulator (a light valve or an image forming device), which forms an image by modulating light according to an image signal, onto a screen from the rear surface of the screen.
As a rear projector, a projector that uses a lens unit to magnify and project an image formed by a light modulating device such as a liquid crystal display (LCD) device or a DMD (digital mirror device) onto a screen from behind the screen is also known. Such rear projectors can produce a large image in spite of being slim in depth, and therefore are being subjected to much attention as next generation image display apparatuses. To display a high-resolution image on a par with a conventional high-resolution television using a rear projector, a lens unit with high optical performance that includes a high aberration-correcting performance and limited fluctuation in focal distance due to temperature is required.
In such a lens unit, there are many lenses to be held by lens holders and there are rising demands on the lens holders used to hold the lenses at predetermined positions. On the other hand, to mass produce rear projectors at low cost as domestic appliances, it is necessary to manufacture lens units with a large number of lenses at low cost and in a short time while maintaining high performance.
Japanese Laid-Open Patent Publication No. H06-138386 discloses a projector where a prism or mirror that bends the optical path is disposed midway in a lens group that composes a lens system to change the optical path.